"He also told me a story which came from his boss"
I don't lend much credence to 3rd hand anecdotes.
"Every so often, another boiler would go ‘boom’. On a regular basis."
On a regular basis? That really does seem unlikely. I think folks would stop doing this after the first house blew up, wouldn't they? Imagine the paperwork!
You burn oil and it heats water until it reaches set temp then the oil gets shut off. Given the stated small characteristic differences between diesel, fuel oil and Jet A1 can't see where this would all go so terribly wrong?